Anti-double stranded (ds)DNA antibodies, a characteristic serologic feature of systemic lupus erythematosus (SLE), are crucial in the pathogenesis of murine lupus nephritis. However, less is understood about the pathogenicity of human anti-DNA antibodies. Furthermore, the mechanisms by which antFDNA antibodies induce renal injury are unclear. We demonstrated that murine anti-dsDNA antibodies directly bind to o_-actinin in renal mesangial cells and podocytes, and that a significant proportion of the anti-dsDNA antibody response in routine lupus is cross-reactive with alpha-actinin. Binding of a pathogenic anti-DNA antibody to mesangial cells induced measurable changes in gene expression. Recently, we isolated several monoclonai human anti-dsDNA antibodies from lupus patients with nephritis. We demonstrated that these antibodies were pathogenic, and induced proteinuda and renal histopathology in mice. These human anti-dsDNA antibodies cross-reacted with alpha-actinin, as well as with other mesangial cell proteins. The goals of this proposal are to study the mechanisms of pathogenicity of human antidsDNA antibodies. We will generate a panel of anti-DNA antibodies from patients with SLE by EBV transformation of peripheral lymphocytes, and determine the renal pathogenicity of these antibodies by injection into SCID mice. We will determine what is the cross-reactive renal antigen for these pathogenic iupus autoantibodies by Western blotting and immunoprecipitations of lysates of human kidney and kidney cell lines. Finally, we will examine if binding of human anti-DNA antibodies to kidney ceils induces alterations in gene expression by microarray analysis of cells treated by pathogenic antibodies cross-reactive with kidney cell-surface proteins.